1. Field of the Invention
The present invention relates to a method for recovering a valuable material from a lithium-ion secondary battery, which is capable of recovering valuable materials, such as cobalt, from defective lithium-ion secondary batteries generated in a production process, lithium-ion secondary batteries, which have been discarded because of end of service life of devices using the batteries or the batteries, and relates to a recovered material obtained by the method for recovering a valuable material from a lithium-ion secondary battery.
2. Description of the Related Art
Lithium-ion secondary batteries have light weight, high volume, and high light in weight, high in volume, and high electromotive force compared to conventional lead storage batteries, or NiCad secondary batteries, and thus are used as a secondary battery for personal computers, electric vehicles, or mobile phones. In a positive electrode of a lithium-ion secondary battery, a valuable material, such as cobalt and nickel, is used as lithium cobalt oxide (LiCoO2), or a ternary positive electrode material (LiNixCoyMnzO2(x+y+z).
Use of lithium-ion secondary batteries is expected to increase in the future. Therefore, it is desired in view of recycling of resources that a valuable material, such as cobalt, is recovered from a defective products generated during production, or lithium-ion secondary batteries discarded due to end of service life of devices using the batteries or the batteries themselves.
When the valuable material is recovered from a lithium-ion secondary battery, it is important that various metals used in the battery are separated and recovered for enhancing a value of a recovered material. Especially, it is very important that the valuable material is separated from iron or the like, and recovered for enhancing a value of a recovered material containing the valuable material.
As for a recovering method for a valuable material, proposed is a method containing; primary roasting a waste lithium secondary battery at temperature of 350° C. or higher; breaking the battery by a shear breaker; sieving the broken product; secondary roasting the undersize particles; treating the roasted particles with acid; adjusting pH of the process liquid to 4 to 5.5 with blowing oxidizing gas into the process liquid, and filtering the process liquid; adding alkali to the filtrate; and further filtering and recovering sedimentary deposits (see Japanese Patent Application Laid-Open (JP-A) No. 07-207349.
Moreover, proposed is a method for recovering cobalt, which contains; roasting a waste lithium secondary battery at temperature of 350° C. or higher; breaking the roasted battery by a shear breaker; sieving the broken product; and subjecting the undersize particles to magnetic sorting (see JP-A No. 07-245126).
In these proposed techniques, however, in the breaking step, the batteries are not broken into the level where a valuable material, such as cobalt, can be sufficiently separated from other metal, such as iron, used for a battery case (housing) at the time of a sieve sorting step, which is a following step. Therefore, a valuable material, such as cobalt, is also remained in the oversize particles after being sieved and sorted. As a result, there is a problem that a recovery rate of a valuable material in a recovered material obtained from the undersize particles is low. Since iron or the like is included in the oversize particles, it is not economical to recover a valuable material from the oversize particles, as many steps are required for recovering the valuable material. In the case where a shear breaker is used, moreover, an iron powder having small particle diameters is generated, and mixed into a recovered material of undersize particles. Since iron and cobalt are both attracted to a magnet, iron is also recovered with cobalt when cobalt is magnetic sorted after the sieve sorting. Therefore, there is a problem that iron is mixed into a recovered material as impurities.
When breaking or sieve sorting is performed by a dry process, moreover, powder dusts, mainly formed of carbon of a negative electrode, are generated, and there is a danger of explosion, which is a problem.
Moreover, proposed is a method containing: decomposing a lithium-ion secondary battery without roasting, followed by separating by means of a ball mill using alcohol (see JP-A No. 2007-122885). In this proposed technique, however, there is a problem that a few separating steps are required, or a problem that iron, which is a metal of a battery case (housing) is crushed, and mixed with a valuable material contained an electrode, so that a large amount of iron is mixed into a recovered material as impurities.
Accordingly, there are currently needs for a method for recovering a valuable material, which can recover a valuable material, such as cobalt, from a lithium-ion secondary battery at a high recovery rate, gives a less contamination amount of impurities, such as iron, to a recovered material containing a valuable material, and has simple steps.